1. Field of the invention
The present invention relates to a method of manufacturing a semiconductor device, and more specifically to a method of forming a metal conductor in a semiconductor device.
2. Description of related art
At present, in most of semiconductor devices including ICs (integrated circuits) to VLSIs (very large scaled integrated circuits), an Al-Si alloy or an Al-Si-Cu alloy has been widely used as a material of a wiring conductor from the standpoint of an ohmic characteristics and an Al spike suppression. However, even if these wiring conductor materials are used, it has not been possible to avoid generation of electromigration and formation of hillock caused by a heat treatment, and therefore, a serious problem has existed in reliability. In order to overcome this problem, it has been proposed to form a wiring conductor of a multilayered structure by using a refractory metal. Nevertheless, it has not been satisfactory.
Recently, it has been proposed to form a wiring conductor of Au (gold). Au is extremely stable from the viewpoint of the wiring conductor material. In addition, anti-electromigration property is as excellent as ten times or more that of an aluminum alloy. Furthermore, Au has high reliability. However, Au is disadvantageous in that an adhesion property to an interlayer film is very poor. Because of this reason, the conventional Au wiring has been realized by providing on an upper surface of an Au wiring conductor a metal film having a good adhesion property to the interlayer film.
However, in a conventional process, it has been difficult to form a metal film on the upper surface of the Au wiring conductor in alignment with the Au wiring conductor. Therefore, if mis-alignment occurs, a short-circuit occurs between wiring conductors or between electrodes. Because of this, it has not been used in a fine pattern wiring. In addition, the conventional process has required a number of steps and has been complicated.
In this connection, a method has been known in which after an electrode or wiring conductor is formed, the electrode or wiring conductor is coated by an electroless plating. This method has been difficult to obtain a complete selectivity, and therefore, could not have been applied to the fine pattern wiring.